Don't think we can help you. We tried to reproduce your problem but could not. The Call function does perform a search for the target file and the FileGet function does not. Another difference is that FileGet supports extended paths and Call does not. Also, FileGet respects IntControl 39 settings, and Call always uses "Read Share mode" to open files. Otherwise, both Call and FileGet use the same internal function to open files.
For what it is worth, the Call function returns a 1400 error when it cannot find the file in the function's first parameter.